Microwave oscillator



Dec. 9, 1 947. I s GUB|N 2,432,193.

MICROWAVE OVSPCIILLATOR Filed Aug. 13, 71943 Patented Dec. 9, 1947 MICROWAVE OSCILLATOR Samuel Gubin, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application August 13, 1943, Serial No. 498,525 4 Claims. (cram-39) This invention relates generally to microwave thermionic tube oscillators and more particularly to an improved oscillator circuit of the grounded anode type.

It is often desirable to employ triodes or other multi-element thermionic discharge tubes rather than magnetrons, or the like, for generating super-high frequency energy. Triodes and similar vacuum tubes have been specially designed for super-high frequency use, but for some applications considerable difficulty has been encountered in providing oscillations at extremely high fre quencies. Triodes of the lighthouse type have been designed to have extremely low electron transit time and low inter-electrode capacities. These tubes have a grid ring seal disposed intermediate the anode and cathode connections. This construction is particularly suited to superhigh frequency circuits of the grounded grid type, which have been used extensively heretofore. In grounded grid oscillation circuits, the natural feedback is through the mesh of the control grid from anode to cathode, This feedback which is a function of the anode to cathode inter-electrode capacitance is usually inadequate to provide stable oscillations, and supplementary external feedback means generally is required.

The use of supplemental feedback means results in two feedback circuit elements which are extremely difficult to adjust over a wide band of frequencies. Under many conditions the two feedback elements aid over a portion of the frequency band and oppose each other over the remaining portion of the frequency band.

Theinstant invention permits the use of such tubes in grounded anode or plate-separation circuits in which there is adequate feedback capacitance within the tube. In circuits of the grounded anode type the feedback path is from control electrode to cathode, and the normal capacitance between these electrodes is relatively large compared to the capacitance between anode and cathode through the grid screen. Since an ample feedback path is provided within the tube, external feedback means are unnecessary to sustain oscillations, and the circuit may be utilized effectively over a relatively wide band of operating frequencies.

A typical embodiment of the invention for use with lighthouse type tubes comprises a cylindrical outer shell completely enclosing the tube and extending axially from both ends thereof. An apertured disc is interposed between the anode terminal of the tube and the cylindrical conductor, In order to provide direct current isolajustment of external feedback means.

tion for the anode voltage, the apertured disc is insulated from the outer cylindrical conductor by means of a mica separator which provides relatively large capacitive coupling between these elements. A smaller concentric cylinder having projecting fingers on one end thereof extending through the apertures of the apertured disc, and separated by air therefrom, is connected to the tube grid terminal. A shorting ring or other tuning means is interposed between the outer and inner concentric cylinders to provide tuning means for the resultant grid-anode cavity, Similarly, a second concentric conductive cylinder is connected to the tube cathode terminal and extends in an opposite direction coaxially with the outer conductive cylinder. A second shorting ring is interposed between the cathode and outer cylindrical conductors for tuning the resultant anode-cathode cavity.

Among the objects of the invention are to provide an improved microwave oscillator of the grounded anode type. Another object of the invention is to provide an improved grounded anode microwave oscillator wherein regeneration is provided by the control electrode-cathode capacitance within the oscillator tube. Another object of the invention is to provide an improved microwave thermionic tube oscillator circuit operable over an extended frequency band without ad- An additional object of the invention is to provide an improved microwave oscillator circuit for ultrahigh frequency tubes having a grid ring seal wherein connections to the tube grid terminal extend through an apertured disc interposed between the tube anode terminal and a cylindrical circuit element at ground potential.

The invention will be further described by reference to the accompanying drawing of which Figures 1 and 2 are cross-sectional elevational views of prior art devices, Figure 3 is a cross-sectional elevational view of the instant invention, and Figure 4 is a cross-sectional view of the device of Figure 3 taken along the section line IV- IV. Similar reference numerals are applied to similar elements throughout the drawing.

. Referring to Figures 1 and 2, two circuits utilized extensively heretofore employ the conventional grounded grid circuitto which the particular conformation of the lighthouse tubes is especially well adapted, In both circuits, the control electrode terminal I of the tube 2 is coupled to a metallic disc 3 and through a relatively large capacitor 4, to a cylindrical circuit element 5 which may be considered to be at ground potential. A second metallic cylinder 6 is connected to the anode terminal 1 of the tube 2 and dis posed concentrically with the grounded cylindrical element 5. A shorting ring or other tuning element 8 is interposed between the anode and circuit elements 5, 6, respectively, for tuning the anode-grid cavity. Similarly, a third cylindrical conductor 9 is connected to the cathode ID of the tube 2 and disposed concentrically with respect to the grounded cylindrical element 5. A second shorting ring or other tuning means II is interposed between the first and third cylindrical circuit conductors 5, 9, respectively, for tuning the resulting grid-cathode cavity. As explained heretofore, external feedback means usually must be employed to provide sustained oscillations of either of these circuits over a relatively wide frequency band, and adjustment of the feedback means is usually necessary as the circuit is tuned over the frequency band. Referring to Figures 3 and 4, the anode terminal l of the tube 2 is 'connected'to an apertured disc I2 having a diameter slightly smaller than the internal diameter of a grounded cylindrical conductor 5. The cylindrical conductor is disposed substantially coaxially with the tube 2. A ring type bracket l3, attached to the inner surface of the grounded cylindrical conductor 5, is separated from the peripheral surface of the apertured disc I 2 by means of a thin mica insulator I l whereby relatively high capacitance is provided between the apertured disc I2 and the grounded cylindrical conductor 5, and effective direct current isolation of the anode voltage is provided.

A second cylindrical conductive element 6 having projecting fingers l6 extending through, but not touching, the sides of the apertures ll of the apertured disc I 2, is connected to the grid terminal l of the thermionic tube 2. The second cylindrical conductor 6 is disposed concentrically within the outer grounded cylindrical conductor 5. A connection is provided from the anode terminal I to a source of unidirectional potential. This connection may be brought out through the interior of the second cylindrical conducting element 6. A shorting ring or other tuning means 8 is interposed between the first and second cylindrical conductors 5, 6, respectively. Adjusting rods l8 connected to the shorting ring 8 provide for adjustment of the position of the shorting ring by any desired external means connected thereto, for tuning the resulting grid anode cavity. I

Similarly, a third cylindrical conductive element 9 is connected to the cathode terminal ll! of the tube 2 and extends in an opposite direction concentrically within the outer grounded cylindrical element 5. A second shorting ring II is interposed between the first and third cylindrical conductive elements 5, 9, respectively. Adjusting rods l9 connected to the second shorting ring ll provide for longitudinal adjustment of the shorting ring to tune the resultant anode-cathode cavity by any desired external means. Filament or heater connections 20 to the tube prongs may be brought out through the interior of the third cylindrical conductive element 9.

Coupling to the oscillatory circuit may be accomplished by inserting a coupling loop 2| into the anode grid cavity intermediate the first and second cylindrical circuit elements, or may be provided in any other manner known'in the art.

Since ample control electrode-cathode capacitance exists within the tube, no external feedback means need be provided. Hence, tuning over the full frequency range of the circuit may be accomplished without adjusting any supplementary feedback devices.

Thus the invention described comprises an improved microwave oscillator circuit of the anode separation type wherein tuning over a wide frequency range may be accomplished without adjustment of supplementary feedback means.

I claim as my invention:

1. An ultra-high frequency oscillator including an electron discharge tube having terminals for an anode, a cathode and a control electrode, a conductive element surrounding said tube and substantially coaxial therewith, capacitive means having apertures therein and connecting said anode terminal to said conductive element, first conductive means connected to said cathode terminal and forming a first adjustable tuned cavity resonator with said conductive element, and second conductive means having restricted portions extending through said apertures of said apertured capacitive means connected to said control electrode terminal and forming a second adjustable tuned cavity resonator with said conductive element, whereby regenerative feedback is substantially provided by the cathode-control electrode capacitance of said tube.

2. An ultra-high frequency oscillator including an electron discharge tube having terminals for an anode, a cathode and a control electrode, a conductive element surrounding said tube and substantially coaxial therewith, capacitive means having apertures therein and connecting said anode terminal to said conductive element, first conductive means connected to said cathode terminal and forming a first adjustable tuned concentric line with said conductive element, and second conductive means having restricted portions extending throughsaid apertures of said apertured capacitive means connected to said control electrode terminal and forming a second adjustable tuned concentric line with said conductive element, whereby regenerative feedback is substantially provided by the cathode-control electrode capacitance of said tube.

3. Apparatus as claimed in claim 1 including adjustable means interposed between each of said conductive means and said conductive element for adjusting the tuning of said first and said second tuned resonators. V

4. Apparatus as claimed in claim 1 including adjustable means interposed between each of said conductive means and said conductive element for adjusting separately the tuning of said first and said second tuned resonators.

SAMUEL GUBIN.

REFERENCES CETED The following references are of record in the file of this patent:

UNITED STATES PATENTS Markowitz Dec. 13, 1928 

